The invention relates to gasoline compositions having improved driveability in a spark-ignited engine.
As is known, inherent in the conventional carburetted multi-cylinder automobile engine are various factors which influence the driveability of the automobile. One such principal factor is the distribution of the air/fuel mixture to the various cylinders through the intake manifold.
In the past any problems arising from the distribution of the fuel in the induction system of the automobile engine has been mitigated or solved by operating the engine on a richer air/fuel mixture, one having a greater than stoichiometric mixture for complete combustion. This mixture was chosen to obtain maximum power with maximum fuel economy.
In order to comply with legislative controls for automotive emission, automotive manufacturers now design automobile engines to operate on leaner air/fuel ratios approaching the stoichiometric mixture, that is, one containing the chemically correct proportions of fuel and air for complete combustion. Although operating with these leaner ratios helps hydrocarbon and carbon monoxide emissions, the problem of cylinder-to-cylinder distribution of the fuel/air mixture is accentuated and it is no longer possible to solve this distribution problem by using richer air/fuel mixtures. Although this lean carburation is a principal factor, it is not the only cause for poor driveability.
Additionally, the engine warm-up period immediately subsequent to cold start is very difficult to control and in the past the choke control was used for a longer period in order to improve driveability during the warm-up period. However, in order to cut back on exhaust emissions, longer choke periods are no longer permissible and the resulting leaner air/fuel mixture used during the warm-up cycle has also accentuated the driveability problem.
The partially-oxidized metal layers comprising the carburetor and intake manifold interior surfaces have critical surface tension and wettability and are completely wetted by any hydrocarbon gasoline component, especially the aliphatic and/or aromatic components. The mixture of gasoline and air that leaves the carburetor and passes to the various cylinders through the intake manifold thereby tends to deposit some of the higher boiling fractions particularly rich in aromatics in the form of a liquid film on these surfaces and particularly on the walls of the intake manifold. For the best distribution of the fuel in the induction system, the gasoline should be present as a vapor or a mist in the air/fuel mixture; therefore, wetting of this surface contributes to less satisfactory distribution and poor driveability.
It has now been found that certain organic compounds which contain fluorine, phosphorus and sulfur inhibit the wetting of the walls of the inlet manifold by gasoline and have a favorable influence on the distribution of the air/fuel mixture to the various cylinders of a multicylinder internal combustion engine.